A latest research has revealed the reason for decreasing water levels in the Caspian Sea, Earth’s largest inland body of water, since the past twenty years.
The increased evaporation over the Caspian Sea has been linked to increased surface air temperatures, likely due to climate change, and the decrease in water levels could threaten shallow spawning grounds for unique species.
Water levels in the Caspian Sea dropped nearly seven centimeters per year from 1996 to 2015, or nearly 1.5 meters total, according to the findings published in the journal Geophysical Research Letters.
According to the data from the study, the average yearly surface temperature over the Caspian Sea rose by about one degree Celsius between the two time-frames studied, 1979-1995 and 1996-2015.
Evaporation brought about by warming temperatures appears to be the primary cause of the current drop in sea level and the decline will likely continue as the planet warms, the researchers said.
“From our point of view as geoscientists, it’s an interesting place because it’s possible to construct a sort of budget for the total amount of water that’s there,” said study co-author Clark Wilson, a geophysicist with the Jackson School of Geosciences at the University of Texas in Austin.
“The real control that causes it to go up and down over long periods of time is really most likely the evaporation, which is almost completely dominated by temperature,” Wilson said.
The Caspian Sea, located between Europe and Asia, covers roughly 371,000 square kilometres. The sea contains oil and natural gas reserves, and is an important resource for fisheries in the surrounding countries.
The researchers looked at the three primary influences on Caspian Sea water levels — water from rivers that drain into the sea, precipitation and evaporation.
They compiled information about water level changes observed by satellites, records of precipitation and drainage into the sea from rivers, and estimations of precipitation and evaporation from climate models.
The researchers then assembled a record of how much each of these factors contributed to observed changes in the Caspian Sea level from 1979 to 2015.
They found Caspian Sea levels increased by about 12 centimetres per year from 1979-1995. But in 1996, sea levels began to drop, and declined by an average of nearly seven centimetres per year through 2015.
Evaporation contributed to about half of that decline, while the combined effects of precipitation and river discharge changes contributed to the other half.
The observed evaporation rates are associated with increased surface air temperature and other climate factors such as surface humidity and wind, the study said.